Method of manufacturing a reservoir tube

Abstract

Reformation of a round tube to a tube with a selected polygonal segment is achieved by supporting the round tube on a mandrel having rounded corners that mate with the tube's inside diameter. The mandrel is otherwise provided in the resultant polygonal shape. The supported tube is subjected to the compressive force of a die having upper and lower die sections that define an elongated polygonal cavity. The planar sides of the cavity are offset relative to the parting line. Preferably, the corners of the cavity adjacent the parting line are wrapped by a leg of the die section. Upon closure of the die sections, the tube material is allocated to a particular quadrant by contact with the die section and the tube is reformed. Excess material that may result from tolerance permitted variations is delivered to the corners of the polygonal tube section maintaining uniform wall thickness across the flat sides of the reformed tube.

What is claimed is: 
     
       1. A method of reforming a round tube to a tube with a selected polygonal segment comprising the steps of: (a) supporting the round tube on a mandrel having rounded corners that closely mate with an inside diameter of the round tube, wherein the mandrel is otherwise substantially provided in a polygonal shape;   (b) subjecting the supported round tube to a compressive force of a die having upper and lower die sections that define an elongated polygonal cavity wherein the cavity has flat sides that are offset relative to a parting line of the upper and lower die sections so that upon closure of the die sections, the tube material is allocated to a particular side of the polygonal shape by contact with the die section wherein the lower die section includes a leg wrapping around a corner of the cavity adjacent the parting line;   (c) reforming the tube to have a polygonal segment with tube side;   (d) delivering excess material that may result from tolerance permitted variations to corners of the polygonal tube section, maintaining uniform wall thickness across the tube sides; and   (e) supporting the round tube by the leg to avoid pinching material in the parting line.   
     
     
       2. A method of reforming a round tube according to claim 1 further comprising the step of: contacting the round tube by the upper and the lower die sections initially at four points that are 45 degrees offset from vertical and horizontal.   
     
     
       3. A method of reforming a round tube according to claim 1 further comprising the step of: closing an end of the round tube prior to supporting the round tube on the mandrel.   
     
     
       4. A method of reforming a round tube according to claim 1 wherein the round tube has an initial outer perimeter distance and further comprising the step of: forming the polygonal segment to have a final outer perimeter distance equal to the initial outer perimeter distance of the round tube.   
     
     
       5. A method of reforming a round tube according to claim 1 further comprising the step of: extending the round tube out from the die so that a round segment remains unreformed.   
     
     
       6. A method of reformation of a round tube to a tube with a selected polygonal segment having flat sides and rounded tube corners comprising the steps of: (a) selecting a tube with a round cylindrical shape and having an inside diameter and an outside diameter;   (b) placing a mandrel having flat sides and rounded mandrel corners into the tube;   (c) supporting the tube on the mandrel so that the rounded mandrel corners closely mate with the inside diameter of the tube;   (d) placing the tube as supported on the mandrel in a die having upper and lower die sections and a parting line between the upper and lower sections wherein the die defines an elongated polygonal cavity having rounded die corners that are offset from the parting line wherein at least one of the die sections has a leg extending around at least one of the rounded die corners that wraps around the rounded die corner;   (e) closing the die so that the upper and lower sections move together;   (f) supporting the tube by the leg to avoid pinching material in the parting line;   (g) allocating an amount of material of the tube to a particular polygonal side by contact between the die and the tube;   (h) compressing the tube so that the inside diameter pulls away from the rounded mandrel corners and moves toward the flat sides of the mandrel;   (i) forming uniformly thick polygonal sides on the tube; and   accommodating excess material at tube corners of the polygonal segment by means of the inside diameter being pulled away from the rounded mandrel corners.   
     
     
       7. A method of reforming a round tube according to claim 6 further comprising the step of: contacting the tube by the upper and the lower die sections initially at four points that are 45 degrees offset from vertical and horizontal.   
     
     
       8. A method of reforming a round tube according to claim 6 further comprising the step of: closing an end of the tube prior to supporting the tube on the mandrel.   
     
     
       9. A method of reforming a round tube according to claim 6 wherein the tube initially has an outer perimeter distance and further comprising the step of: forming the polygonal segment to have an outer perimeter distance equal to the initial outer perimeter distance of the tube.   
     
     
       10. A method of reforming a round tube according to claim 6 further comprising the step of: extending the tube out from the die so that a round segment remains unreformed.   
     
     
       11. A method of reformation of a round tube to a tube with a selected polygonal segment having flat sides and corners to produce a reservoir tube for a suspension damper comprising the steps of: (a) selecting a tube of a round cylindrical shape with an inside diameter and an outside diameter;   (b) closing an end of the tube with a circular end;   (c) placing a mandrel in the tube, wherein the mandrel has a polygonal cross section with a plurality of flat sides and with a plurality of rounded mandrel corners at junctures between the flat sides, wherein the rounded mandrel corners lie on a diameter that substantially corresponds with the inside diameter of the tube;   (d) positioning the tube and the mandrel in a die having an upper die section and a lower die section defined on opposed sides of a parting line, wherein the lower die section defines a cavity with planar sides that are disposed at angles relative to the parting line, wherein the tube is positioned so that the circular end extends out of the cavity, and wherein the planar sides meet at rounded die corners and wherein two of the rounded die corners are positioned near the parting line and off-center relative to the parting line so that the die defines a pair of legs that wrap around the two rounded die corners at the parting line;   (e) closing the die so that the upper and lower die sections come together, wherein the planar sides meet the round cylindrical tube at tangent points redistributing the round cylindrical tube so that the inside diameter pulls away from the rounded mandrel corners and moves toward the flat sides of the mandrel;   (f) compressing the round cylindrical tube between the flat sides of the mandrel and the planar sides of the die cavity so that a polygonal segment is formed on the tube wherein the polygonal segment has tube sides with a substantially consistent thickness; and   (g) moving the die to a closed position where the rounded die corners and rounded mandrel corners are substantially aligned and accommodating excess material at a plurality of tube corners formed between the tube sides of the polygonal segment and between the rounded die corners and the rounded mandrel corners.   
     
     
       12. A method of reformation of a round tube according to claim 11 further comprising the step of: supporting the tube by the legs of the die to avoid pinching material in the parting line.   
     
     
       13. A method of reforming a round tube according to claim 11 further comprising the step of: contacting the round tube by the upper and the lower die sections initially at four points 45 degrees offset from vertical and horizontal.   
     
     
       14. A method of reforming a round tube according to claim 13 further comprising the step of: applying a symmetrical load to the tube at the 45 degree points to allocate tube material to form a particular tube side and evenly distribute tube material around the mandrel.   
     
     
       15. A method of reforming a round tube according to claim 11 wherein the round tube has an outer perimeter distance and further comprising the step of: forming the polygonal segment to have an outer perimeter distance equal to the outer perimeter distance of the round tube.   
     
     
       16. A method of reforming a round tube according to claim 11 wherein the tube has an open end adjacent the circular end, and further comprising the step of: positioning the tube in the die so that the open end extends from the cavity wherein a round segment remains on the tube adjacent the open end.   
     
     
       17. A method of reforming a round tube according to claim 11 wherein the tube selected in step (a) has an outside diameter equal to an inside perimeter of the cavity of the upper and the lower die sections. 
     
     
       18. A method of reforming a round tube according to claim 11 wherein when the inside diameter of the tube pulls away from the rounded mandrel corners in step (e), the inside diameter pulls away from opposite edges of any two adjacent rounded mandrel corners.